Electromagnetic wave absorber, method of manufacturing the same and appliance using the same

ABSTRACT

An object of the present invention is to provide an electromagnetic wave absorber which is excellent in the electromagnetic wave absorbing characteristics in the high frequency range above 1 GHz, and to provide a method of manufacturing the electromagnetic wave absorber and appliances using the electromagnetic wave absorber.  
     An electromagnetic wave absorber and a composite member in accordance with the present invention are characterized by that magnetic metal grains are covered with ceramic above 20 volume %. Further, a method of manufacturing the electromagnetic absorber and the composite member is characterized by that composite magnetic particles, in which a plurality of magnetic metal grains and ceramic are unified, are formed through the mechanical alloying method of a composite powder composed of magnetic metal powder and ceramic powder.  
     Further, the present invention exists in a semiconductor device, an optical sending module, an optical receiving module, an optical sending and receiving module, an automatic tollgate preventing erroneous operation due to electromagnetic wave disturbance which use the electromagnetic wave absorber.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a novel electromagnetic waveabsorber, a method of manufacturing the electromagnetic wave absorber, acomposite member and an appliance of the electromagnetic wave absorber,and particularly to an electromagnetic wave absorber comprisingcomposite magnetic particles composed of magnetic metal grains andceramics, particularly, fine crystalline grains containing at least onekind of material selected from the group consisting of non-magnetic orsoft magnetic metal oxides, carbides and nitrides, and a method ofmanufacturing the electromagnetic wave absorber, a composite memberusing the electromagnetic wave absorber, and a semiconductor device, aprinted wire board, an optical sending and receiving module, anelectronic tall collection system and electronic device casing using themagnetic metal particles.

[0003] By the present invention, an optical sending module, an opticalreceiving module or an optical sending and receiving module integratingthe optical sending module and the optical receiving module used in ahigh speed communication network using optical fibers can be obtained,and the modules can be made small in size, light in weight, high inprocessing speed and high in sensitivity by suppressing noises emittedto the outside and noise interference inside the module.

[0004] 2. Description of the Prior Art

[0005] In recent years, the tendency of high speed processing in theelectronic equipment is being accelerated, and the operating frequencyof an IC such as an LSI or a microprocessor is being rapidly increased,and accordingly unnecessary noises are likely to be emitted.

[0006] Further, in the field of communication, the GHz bandelectromagnetic waves are used in the next generation multimedia mobilecommunication (2 GHz) and in wireless LANs (2 to 30 GHz). In the fieldof the Intelligent Transport System (ITS), the Electronic TollCollection System (ETC) uses 5.8 GHz electromagnetic wave, and theAdvanced Cruise-assist Highway System (AHS) uses 76 GHz electromagneticwave. It is expected that the range of use of the high frequencyelectromagnetic waves will be rapidly expand further wider in thefuture.

[0007] As the frequency of electromagnetic wave is increased, theelectromagnetic wave is apt to be emitted as a noise. On the other hand,in the recent electronic equipment, by decrease of the noise margin dueto reducing of electric power consumed by the equipment and by decreaseof immunity (noise resistance) due to replacement of digital circuits toanalogue circuits and the tendency of small-sizing and high-mountingdensity, the noise environment inside the equipment is deteriorated tocause a problem of erroneous operations of the equipment due toelectromagnetic interference (hereinafter, referred to as EMI).

[0008] Therefore, measures are taken to reduce the EMI inside theelectronic equipment by placing an electromagnetic wave absorber in theelectronic equipment. As an electromagnetic wave absorber for GHz band,a sheet composed of an electrically insulating organic material such asrubber, a resin or the like and a magnetic lossy material such as a softmagnetic metal oxide, a soft magnetic metallic material or the like ismainly used.

[0009] However, the electric resistivity is around 500 to 1000 μΩ·cmwhich is not so high. Therefore, decrease of the magnetic permeabilitydue to eddy current in the GHz region is inevitable. Further, in regardto the complex specific dielectric constant, since the imaginary part islarge compared to the real part because the electric resistivity is notsufficiently high, it is difficult to adjust the impedance matching.

[0010] In general, characteristics required for the electromagnetic waveabsorber for electronic information-and-communication equipment are{circle over (1)} a large reflection attenuation coefficient (smallreflection coefficient), {circle over (2)} a wide band capable ofabsorbing electromagnetic wave, and {circle over (3)} thin thickness.However, no electromagnetic wave absorber capable of satisfying all thecharacteristics has been materialized yet.

[0011] In order to attain the above item {circle over (1)}, it isnecessary that the amount of electromagnetic wave reflected on thesurface of the absorber is made small. In order to do so, it isnecessary to make the value {square root}(μ_(r)/ε_(r)) of characteristicimpedance of the substance close to the value {square root}(μ₀/ε₀) ofcharacteristic impedance of the free space. Therein, μ_(r) is a complexspecific magnetic permeability μ_(r)(μ_(r)′+jμ_(r)″), ε_(r) is a complexspecific dielectric constant ε_(r)(ε_(r)′+jε_(r)″), and μ₀ and ε₀ arethe magnetic permeability and the dielectric constant of the free space,respectively. In order to attain the above item {circle over (2)}, it isnecessary that the values μ_(r)′ and μ_(r)″ are gradually monotonouslydecreased with respect to frequency while the relationship between thevalues μ_(r)′ and μ_(r)″ is being kept nearly constant. In order toattain the above item {circle over (3)}, it is necessary that the amountof attenuation of electromagnetic wave inside the substance is madelarge. In order to do so, it is necessary that the real part of thepropagation constant (γ=2πf(μ_(r), ε_(r))^(0.5)) of the substance islarge, that is, the values of the complex specific magnetic permeabilityand the complex specific dielectric constant at a desired frequency aremade large. However, as the value of the complex specific magneticpermeability becomes large, it is difficult to adjust the impedancematching of the substance with the free space.

[0012] Since the soft magnetic metal oxide material of spinel crystalstructure as a proven electromagnetic absorber has an electricresistivity extremely higher than that of the soft magnetic metallicmaterial, the magnetic permeability rapidly decreases in the GHz bandthough the reflection by eddy current is small. Therefore, aconsiderably thick thickness is required in order to well absorb theelectromagnetic wave.

[0013] On the other hand, the soft magnetic metallic material haspossibility of materializing a thin electromagnetic wave absorberbecause the specific magnetic permeability is very high. However, in thehigh frequency region, the specific magnetic permeability issubstantially decreased and the imaginary part of the complex specificdielectric constant is substantially increased due to eddy current lossbecause the electric resistivity is low. Therefore, the reflectionbecomes large, and the soft magnetic metallic material does not work asan electromagnetic wave absorber.

[0014] In order to solve the problem described above, Japanese PatentApplication Laid-Open No.9-181476 proposes to use an ultra-finecrystalline magnetic film of a hetero-granular structure in whichferromagnetic ultra-fine crystalline metallic phases are dispersed in ametal oxide phase as an electromagnetic wave absorber in a highfrequency range. Such a magnetic film is characterized that the softmagnetism is materialized by the ferromagnetic ultra-fine crystals andthe high electrical resistivity is materialized by the metal oxidephase, and thereby the eddy-current loss is reduced and the highmagnetic permeability in the high frequency range can be obtained.

[0015] The method of manufacturing the electromagnetic wave absorber isthat the soft magnetic metal and oxygen, nitrogen, carbon are sputteredtogether with a metal oxide phase constitutive element having anaffinity with the above elements at a time to form an amorphous filmcontaining these elements on a substrate such as an organic film, andthen the film is heat-treated to form the two-phase structure byproducing the ferromagnetic ultra-fine crystals in the metal oxidephase. However, the electromagnetic wave absorber has problems in thatthe cost is high because a large film-forming apparatus is required, andthat use of the electromagnetic wave absorber is limited because of thethin-film structure.

[0016] Japanese Patent Application Laid-Open No.7-212079 and JapanesePatent Application Laid-Open No.11-354973 disclose an electromagneticwave interference suppresser or an electromagnetic wave absorbercomposed of oblate shaped soft magnetic metal particles and organicbond. The soft magnetic metal particle is formed in an oblate shapehaving a thickness thinner than the skin depth to suppress eddy current,and improvement of magnetic resonance frequency is achieved by theeffect of shape magnetic anisotropy, and improvement of magneticpermeability is achieved by reducing of the demagnetization field causedby the shape. As the result, an excellent electromagnetic waveabsorption ability is obtained in the range of several MHz to 1 GHz.However, it is not sufficient in the thickness and the absorptionability as an electromagnetic wave absorber used inside an electronicequipment or used for high frequency region.

[0017] Further, Japanese Patent Application Laid-Open No.9-111421proposes a magnetic material for loading coils which obtains highelectric resistivity in a high frequency region by heat-treating a highmagnetic-permeability amorphous alloy at a temperature above thecrystallization temperature in an atmosphere containing at least onekind selected from the group consisting of oxygen gas, nitrogen gas andammonia gas to form crystal grains made of the high magneticpermeability alloy and oxide or nitride around the crystal grains.

[0018] Furthermore, Japanese Patent Application Laid-Open No.11-16727proposes a magnetic thin film for high frequency magnetic elementscomposed of iron having ferromagnetism and nickel ferrite havingmagnetism, and having a structure of dispersing a magnetic phase in aferromagnetic phase or the ferromagnetic phase in the magnetic phase, orlaminating the ferromagnetic phase and the magnetic phase in amultilayer. However, the gazette does not proposed to use the magneticthin films as an electromagnetic wave absorber.

[0019] Further, Japanese Patent Application Laid-Open No.9-74298proposes an electromagnetic wave shield material formed by mixingceramic and magnetic grains in a ball mill using silicon nitride ball,and then sintering the mixture. However, the gazette does not proposedany electromagnetic wave absorber.

[0020] Further, in regard to the optical sending and receiving module, apreventive measure of internal interference caused by sending andreceiving of noises between the optical sending part and the receivingpart is disclosed in Japanese Patent Application Laid-Open No.11-196055.

SUMMARY OF THE INVENTION

[0021] An object of the present invention is to provide a thinelectromagnetic wave absorber which is excellent in the electromagneticwave absorbing characteristics in the high frequency range and ismanufacture through less number of production processes, and to providea method of manufacturing the electromagnetic wave absorber, a compositeusing the electromagnetic wave absorber, and appliance using theelectromagnetic wave absorber.

[0022] Another object of the present invention is to provide an opticalsending module, an optical receiving module and an optical sending andreceiving module which can be made small in size, light in weight, highin processing speed and high in sensitivity using an electromagneticwave absorber which has good applicability, and has electromagnetic waveabsorption characteristics not to be deteriorated even in a condition oftransmission speed above 2.4 GHZ.

[0023] An electromagnetic wave absorber in accordance with the presentinvention is characterized by that the electromagnetic wave absorbercomprises composite magnetic particles preferably having a grain sizesmaller than 10 μm, particularly preferably smaller than 5 μm, in whichmagnetic metal grains and ceramic are unified, preferably, magneticmetal grains and ceramic above 10%, preferably above 20%, in volumeratio are unified; and by that composite magnetic particles in which aplurality of fine magnetic metal grains and ceramic are unified byenclosing the plurality of fine magnetic metal grains with the ceramic;and by that composite magnetic particles in which a plurality ofmagnetic metal grains and ceramic are unified by embedding ceramics,preferably in a form of bar-shape, into magnetic metal grains.

[0024] That is, an electromagnetic wave absorber in accordance with thepresent invention is characterized by that the electromagnetic waveabsorber comprises composite magnetic particles in which a large numberof fine magnetic metal grains, preferably smaller than 0.1 μm,particularly preferably smaller than 50 nm, and ceramic above 10 volume%, preferably 20 to 70 volume %, are unified. Particularly, the magneticmetal and the ceramic are formed in alternatively laminated layers ineach grain, and the magnetic metal is of a form of complicated shapedparticles, and the size of most of the particles is smaller than 100 nm,and the particle is enclosed with the ceramic. The complicated shapedparticle is formed by gathering fine particles having a particle sizesmaller than 20 nm. Most of the ceramic is firmed in a shape surroundingthe magnetic particles, and a small amount of the ceramic is formed inbar-shaped grains.

[0025] It is preferable that the magnetic metal is at least one kind ofmetal or alloy selected from the group consisting of iron, cobalt andnickel, and the ceramic is at least one kind of ceramic selected fromthe group consisting of oxide, nitride and carbide of iron, cobalt,nickel, titanium, barium, manganese, zinc, magnesium, aluminum, silicon,and copper; or that the ceramic particles are bonded onto the surface ofthe composite magnetic particle to unify the ceramic particles and thecomposite magnetic particles; or that most of the ceramic particlesexist inside the crystalline grain and the grain boundary of themagnetic metal grains. It is preferable that the magnetic metal is asoft magnetic metal.

[0026] Further, the composite magnetic particle in the present inventionis a composite magnetic particle in which the magnetic metal particleand the ceramic are unified by embedding and mixing finely in nm-orderthe grains of ceramic such as metal oxide inside the magnetic metalparticle of soft magnetic ultra fine crystals. The high magneticpermeability obtained by finely crystallizing the soft magnetic metaland the high electric resistivity obtained by dispersing the ultra-fineceramic grains are materialized at a time. Therefore, the high magneticpermeability can be maintained and the better absorbing characteristicsare also maintained even in the high frequency region.

[0027] Further, since the composite magnetic particle has a form ofalternatively laminating the soft magnetic metal phase and the metaloxide phase, the width of the soft magnetic metal phase becomes belowthe skin depth and accordingly there is an effect equivalent todispersing soft magnetic metal powder having a thickness below the skindepth. Therefore, the eddy current can be reduced, and theelectromagnetic wave can be efficiently taken in. Further, by changingthe mixing ratio and the combination of the metal oxide phase and theferromagnetic ultra-fine crystalline metallic phase, the parametersrelating to the characteristic of electromagnetic wave absorption ofcomplex specific magnetic permeability and the complex specificdielectric constant can be comparatively freely controlled, andtherefore, better characteristic of electromagnetic absorption can beobtained in a target frequency band.

[0028] In regard to the mixing ratio of the added ceramic particles,when the volumetric mixing ratio of ceramics is below 20 volumetric % tothat of the soft magnetic metal particles, the electric resistivity isnot improved sufficiently. Further, when the volumetric mixing ratio ofnon-magnetic ceramics is above 80 volumetric %, the magneticpermeability of the composite magnetic particles is decreasedexcessively low to deteriorate the characteristic of electromagneticwave absorption. From these facts, it is preferable that the volumetricmixing ratio of ceramics is 30 to 60 volumetric %.

[0029] In the present invention, the magnetic metal powder and theceramic powder are unified by mixing them with each other in anultra-fine state through the mechanical alloying method. The method ofmanufacturing an electromagnetic wave absorber in accordance with thepresent invention is characterized by that the composite magneticparticles, in which the magnetic metal grains and the ceramic,preferably, above 10% in volume ratio are unified, are formed. Further,the method of manufacturing an electromagnetic wave absorber inaccordance with the present invention is what is called as themechanical alloying method in which a composite powder composed of themagnetic metal powder and the ceramic powder, and metallic balls orceramic balls, size of the ball being larger than grain size of themetallic powder, an amount of the balls being larger than an amount ofthe composite powder, preferably, a ratio of 50 to 100 of balls to 1 ofthe composite powder in weight are contained into a pot, and the pot isrotated at a high speed, preferably 1500 to 3000 rpm to mix and unifiesthe magnetic metal powder and the ceramic powder in an ultra-fine stateby add strong energy to the powders. By the method, the compositemagnetic particles in which the plurality of fine magnetic metal grainsand ceramic are unified are formed.

[0030] That is, the method of manufacturing the electromagnetic absorberin accordance with the present invention characterized by that thecomposite magnetic particles, in which more than 10% of the ultra-finemagnetic metal grains and the ceramic particles are dispersed, areformed through the method generally called as alloying method in whichthe composite powder composed of the magnetic metal powder and theceramic powder is mixed and unified into an ultra-fine state. Since thecomposite magnetic particles have a high electric resistivity in thehigh frequency region by forming the ultra-fine state, a high magneticcharacteristic can be obtained. Therefore, high electromagnetic waveabsorption characteristic can be obtained.

[0031] The electromagnetic wave absorber in accordance with the presentinvention is characterized by that the composite magnetic particlesdescribed above, preferably, 20 to 70 weight % of the composite magneticparticles are dispersed in a material having an electric resistivityhigher than an electric resistivity of the composite magnetic particles,particularly, a resin, an insulation paint or a ceramic sinteredmaterial. Therein, the reason why the composite magnetic particles aredispersed in a material having an electric resistivity higher than thatof the composite magnetic particles is that the electric resistivity ofthe composite magnetic particle itself is not small enough to besatisfied as the electromagnetic wave absorber, and that the freedom ofdesigning the electromagnetic wave absorber is increased by changing themixing ratio of the composite magnetic particles. It can be said fromthe viewpoint that the composite magnetic material is better in aparticle form than in a thin film form.

[0032] From the above, the electromagnetic wave absorber in accordancewith the present invention composed of the composite magnetic particlescan be widely used in various use, for example, radiating noise in asemiconductor element level can be prevented by mixing theelectromagnetic wave absorber in a sealing resin of a resin sealing typesemiconductor package; or electromagnetic wave generated in anelectronic circuit board itself can be absorbed by mixing theelectromagnetic wave absorber into an electronic circuit board made ofresin or an electronic circuit board made of ceramic of a meal oxide; orinternal interference can be prevented by applying the electromagneticwave absorber together with an insulation paint onto an inner surface ofan electronic casing made of a metal.

[0033] A composite member in accordance with the present invention ischaracterized by that the composite member comprises the compositemagnetic particles having a grain size smaller than 10 μm in which theplurality of magnetic metal grains ceramic above 20% in volume ratio areunified; or the composite magnetic particles in which the plurality offine magnetic metal particles and the ceramic are unified by enclosingthe plurality of fine magnetic metal grains with the ceramic; or thecomposite magnetic particles in which the magnetic metal grains and theceramic are unified by embedding bar-shaped ceramics into the magneticmetal grains.

[0034] A composite member in accordance with the present invention ischaracterized by that the composite member comprises any one of orcombination of the composite magnetic particles having a grain sizesmaller than 10 μm in which the magnetic metal grains and the ceramic,preferably above 10% in volume ratio, are unified; and the compositemagnetic particles in which the plurality of fine magnetic metalparticles and the ceramic are unified by enclosing the plurality of finemagnetic metal grains with the ceramic; and the composite magneticparticles in which the magnetic metal grains and the ceramic are unifiedby embedding ceramics into the magnetic metal grains. The compositemember can be manufactured through a method similar to that describedabove.

[0035] The present invention relates to a composite member formed bycompounding composite magnetic particles, in which magnetic metal grainsand ceramics are unified, and a material having an electric resistivityhigher than that of the composite magnetic particle.

[0036] Further, the present invention relates to a composite memberformed by compounding composite magnetic particles, in which magneticmetal grains and ceramics are unified, and at least one kind of a resinhaving an electric resistivity higher than that of the compositemagnetic particle alumina and silica.

[0037] It is preferable that the ceramic is contained 10 to 75 vole % inthe composite magnetic particle, and is of granular structure dispersedin the magnetic metal grains. Further, in the present invention, it ispreferable that the composite magnetic particles are formed by unifyingfine crystals of a magnetic metal having an average grain size below 50nm, preferably, below 20 nm and ceramics of above 10 volume %,preferably, 15 to 70 volume %, and that an average crystal grain size ofthe composite magnetic particle is smaller than 50 nm. Further, thematerials of the magnetic metal grains and the ceramic are the same asdescribed above.

[0038] The electromagnetic wave absorber is characterized by that thesurface of the composite magnetic particle is coated with a materialhaving an electric resistivity higher than an electric resistivity ofthe composite magnetic particle; and that the composite magneticparticle has an aspect ratio larger than 2, and has an oblate shape; andthat the composite magnetic particles are uniformly dispersed in thematerial having the high electric resistivity; and that the oblatecomposite magnetic particles are oriented in one direction in thematerial having the high electric resistivity; and that the materialhaving the high electric resistivity is a polymer material or a ceramicsintered material.

[0039] By forming the composite magnetic particle so as to have thestructure that the ceramic phase having the high electric resistivityencloses around the ultra-fine magnetic metal crystals, as describedabove, the electric resistivity can be improve in the GHz regioncompared to the single phase metal particle, and in addition the complexspecific magnetic permeability can be also improved.

[0040] Therein, when the crystal grain size of the magnetic metalcomposing the composite magnetic particle, the exchange interactionbetween metal crystals is weakened to deteriorate the soft magneticcharacteristic. Therefore, the magnetic permeability is decreased, andthe electric resistivity is increased.

[0041] As the result, the crystal grain size of the magnetic metalcomposing the composite magnetic particle in the present invention ispreferably below 50 nm, particularly preferably below 20 nm.

[0042] Further, by controlling the volume ratio of the ceramics in thecomposite magnetic particle, the parameters relating to theelectromagnetic wave absorption characteristic of the complex specificmagnetic permeability and the complex specific dielectric constant canbe controlled. Therefore, a good electromagnetic wave absorptioncharacteristic in a target frequency band can be obtained. When thevolumetric mixing ratio of ceramic to the magnetic metal is below 10volume %, the complex specific magnetic permeability becomes highbecause the electric resistivity is not sufficiently increased, but thecomplex specific magnetic permeability is rapidly decreased in the GHzregion because of eddy current loss. Further, the imaginary part of thecomplex specific dielectric constant becomes too large to obtainsufficient electromagnetic wave absorption characteristic. Particularlyin the case where the ceramic phase is non-magnetism, when thevolumetric mixing ratio of the ceramic exceeds 70 volume %, the realparts of the complex specific magnetic permeability and the complexspecific dielectric constant of the composite magnetic particle aredecreased too low. Therefore, in order to obtain sufficientelectromagnetic wave absorption characteristic, the electromagnetic waveabsorber needs to have a rather thick thickness. From the above reason,it is preferable that the volumetric mixing ratio of the ceramic is 15to 70 volume % to the soft magnetic metal grains.

[0043] The electromagnetic wave absorber in accordance with the presentinvention is characterized by that the composite magnetic particles of,preferably, 20 to 80 volume % are dispersed in a materal having anelectric resistivity higher than the composite magnetic particle,particularly, a resin, an insulation paint or a ceramic sinteredmaterial.

[0044] In the present invention, by forming the composite magneticparticle so as to have the structure that the ceramic phase having thehigh electric resistivity encloses around the fine magnetic metalcrystals, the electric resistivity can be improve in the GHz regioncompared to the commonly used single phase metal particle, and inaddition the complex specific magnetic permeability can be alsoimproved.

[0045] Further, by controlling the volume ratio of the ceramics in thecomposite magnetic particle, the parameters relating to theelectromagnetic wave absorption characteristic of the complex specificmagnetic permeability and the complex specific dielectric constant canbe controlled. Therefore, a good electromagnetic wave absorptioncharacteristic in a target frequency band can be obtained. When thevolumetric mixing ratio of the ceramic phase to the magnetic metal phaseis below 20 volume %, the electric resistivity is not sufficientlyincreased. Particularly, when the volumetric mixing ratio of the ceramicexceeds 70 volume %, the magnetic permeability of the composite magneticparticle is decreased too low. Therefore, the thickness of theelectromagnetic wave absorber can not be made thinner. From the abovereason, it is preferable that the volumetric mixing ratio of the ceramicis 20 to 70 volume % to the soft magnetic metal grains.

[0046] The reason why the composite magnetic particles are dispersed inthe material having an electric resistivity higher than that of thecomposite magnetic particle is {circle over (1)} that the electricresistivity of the composite magnetic particle itself is notsufficiently high as the electromagnetic wave absorber, and {circle over(2)} that the real part of the complex specific dielectric constant canbe made large because a micro capacitor using the composite magneticparticle as the electrode is formed, and {circle over (3)} that thefrequency characteristics of the complex specific magnetic permeabilityand the complex specific dielectric constant can be controlled bycontrolling the particle shape and the dispersing form of the compositemagnetic particles, and {circle over (4)} that the frequencycharacteristics of the complex specific magnetic permeability and thecomplex specific dielectric constant can be controlled by controllingthe volumetric mixing ratio of the composite magnetic particles to theinsulation resin.

[0047] In the present invention, the three phase structure of themagnetic metal phase, the high electric resistivity ceramic phase andthe insulation material which is formed by unifying the compositemagnetic particles with the insulation material having an electricresistivity higher than that of the composite magnetic particle ispreferable compared to the two layer structure such as the compositebody of magnetic metal single phase particles and insulation resin orthe composite body of magnetic metal single phase particles and ceramic.

[0048] Therein, in order to further improve the electromagnetic waveabsorption characteristics, it is preferable that the shape of thecomposite magnetic particle is formed in an oblate shape having anaspect ratio larger than 2 and a thickness thinner than the skin depth,and the oblate composite magnetic particles are orientated in thematerial having the high electric resistivity. That is, theelectromagnetic wave absorption characteristics can be further improvedand thinning of the electromagnetic wave absorber can be attained bysuppressing of the rapid decrease in the complex specific magneticpermeability due to eddy current, and by increasing of the magneticpermeability by decreasing the effect of demagnetizing field due to theparticle shape and increasing of the magnetic resonance frequency by theshape magnetic anisotropy, and by improving the real part of the complexspecific dielectric constant by increasing the area of the capacitorelectrodes.

[0049] The methods of unifying the fine crystal grains of the magneticmetal (hereinafter, referred to as magnetic metal grains) and theceramic applicable to the present invention are as follows. That is, themechanical alloying method; and a method that an alloy powder, which iscomposed of a magnetic metal and an element having an affinity withoxygen, nitrogen and carbon higher than the magnetic metal and has ahigh content of any one of these gas elements, is fabricated through theatomizing method, and then the soft magnetic metal phase and the ceramicphase are separately produced by performing heat treatment of the alloypowder; and a method that an alloy powder, which is composed of amagnetic metal and an element having an affinity with oxygen, nitrogenand carbon higher than the magnetic metal and has a high content of anyone of these gas elements, is fabricated through the atomizing method,and then heat treatment of the alloy powder is performed in a gasatmosphere containing any one of oxygen, nitrogen and carbon; and amethod that the soft magnetic metal phase and the ceramic phase areseparately produced; and a sol-gel method using metal alkoxide. Themanufacturing method is not limited to the above-described methods, buta manufacturing method capable of finally obtaining the compositemagnetic particles composed of the magnetic metal grain phase and thehigh electric resistivity ceramic phase.

[0050] In order to increase the electric resistivity of the compositemagnetic particle itself, it is possible that a high electricresistivity film such as an oxide film or a nitride film is formed onthe surface of the composite magnetic particle at the same timeproducing the composite magnetic particles.

[0051] Further, it is possible to coat the surface of the compositemagnetic particle with a material having a higher electric resistivitythrough a mechanical unifying method, preferably through themechano-fusion method using a kind of shearing type mill.

[0052] The composite magnetic particles are kneaded with an insulationpolymer material of 30 to 80 volume %. As the preferable insulationpolymer materials are polyester group resins; polyvinyl chloride groupresins; polyvinyl butylal resin; polyurethane resin; cellulose groupresins; copolymer of these resins; epoxy resin; phenol resin; amidegroup resins; imide group resins; nylon; acrylic resin; syntheticrubber; and so on. Epoxy resin is preferable. When the volumetricfilling ratio of the composite magnetic particles to the resin is above50 vol %, the electric resistivity of the resin composite body isdecreased due to contact between the composite magnetic particlesthemselves. Therefore, it is necessary to add, at a time, a couplingtreatment agent of silane group, alkylate group or titanate group, or amagnesium phosphate-borate insulation treatment agent.

[0053] As described above, by coating the surfaces of the compositemagnetic particles with the high electric resistivity material using thesurface oxidation method, the mechanical unifying method or the chemicalsurface treatment method solely or in combination, the real parts of thecomplex specific magnetic permeability and the complex specificdielectric constant can be improved and the electromagnetic waveabsorptivity can be improved with keeping the electric resistivity at aconstant value even if the mixing ratio of the composite magneticparticles to the resin is increased.

[0054] The following applications of the electromagnetic wave absorberof the present invention are considered.

[0055] (1) In a semiconductor integrated device of resin seal type, thecomposite magnetic particles are mixed in the sealing resin to suppressradiant noises in a semiconductor 110 element level.

[0056] (2) In a printed wiring board, the paint comprising theelectromagnetic wave absorber of the present invention is directlyapplied or a film formed the paint into a sheet-shape is attached onto apart of or the whole of both of the surface having a wiring circuitformed thereon and the surface of the insulation board not having thewiring circuit to form an electromagnetic wave absorption layer.Thereby, occurrence of noises such as a cross-talk phenomenon due toelectromagnetic wave generated from the printed wiring circuit board canbe suppressed. Particularly, high density and high integration of amultilayer wiring circuit board can be attained with high reliability.Wherein, the multi-layer wiring circuit board is that a first-layerwiring layer is formed at least one side main surface of thesemiconductor board, an insulation film being formed on the surface ofthe first-layer wiring layer, a second-layer wiring layer electricallyconnected to the first-layer wiring layer through a via-hole beingformed on the insulation film, this laying process being repeated toform multi-layer wiring circuits.

[0057] (3) A cap made of the composite magnetic particles and thematerial having an electric resistivity higher than that of thecomposite magnetic particle is mounted on a printed wiring board so asto enclose a semiconductor element of noise source. Thereby, theelectromagnetic wave emitted from the semiconductor element can beefficiently absorbed and the electromagnetic wave internal interferencecan be suppressed.

[0058] The insulation paint containing the composite magnetic particlesis applied onto the inner surface of a metal electronic equipmentcasing, or an electronic equipment casing formed of the compositemagnetic particles and resin is used. Thereby, the electromagnetic waveinternal interference can be suppressed.

[0059] Further, the present invention is characterized by asemiconductor device in which a semiconductor element mounted on aprinted wiring board is sealed with a resin containing anelectromagnetic wave absorber, wherein the resin in the side of theelement is covered with a resin free from the electromagnetic waveabsorber. The present invention is also characterized by a printedwiring board comprising a wiring circuit on an insulation board, and thecircuit is covered with an insulation layer, wherein layers comprisingan electromagnetic wave absorber are formed on a surface of theinsulation board opposite to the surface having the wiring circuitformed and on the insulation layer.

[0060] Further, the semiconductor device of the present invention isthat a semiconductor element mounted on a printed wiring board iscovered with a metal cap of which an inner peripheral surface is formedof an electromagnetic wave absorber; or that a semiconductor elementmounted on a printed wiring board is covered with a cap having anelectromagnetic wave absorber; or that a printed wiring board and asemiconductor element mounted on the board are covered with a casinghaving an electromagnetic wave absorber. It is preferable that thematerial described above is used for the electromagnetic wave absorberused in each of the semiconductor devices of the present invention.

[0061] In the present invention, in an optical sending or receivingmodule comprising an electric-optical converter used for a high speedcommunication network, by covering an optical sending element or anoptical receiving element and the related circuit with anelectromagnetic wave absorber having the composite magnetic particlesand the ceramic, or with an electromagnetic wave absorber in which thecomposite magnetic particles and a material having an electricresistivity higher than that of the composite magnetic particle areunified, the electromagnetic wave emitted outside the module and thenoise interference inside the module can be suppressed. Theelectromagnetic wave absorber used in the present invention is the sameas described above.

[0062] According to the present invention, the electromagnetic waveabsorber composed of the composite magnetic particles in which themagnetic metal and the non-magnetic or magnetic ceramics are unified inultra-finely dispersing can obtain the remarkable effect having anexcellent electromagnetic wave absorption characteristic compared to theelectromagnetic wave absorber made of the simply mixed powder.

[0063] Further, according to the present invention, the electromagneticwave absorber is formed by unifying the composite magnetic particles,each of which is composed of fine crystal grains of the magnetic metal(the magnetic metal grains) and the ceramic phase, particularly, finecrystal grains including at least one kind of non-magnetic or magneticoxide, carbide and nitride, and the material having an electricresistivity higher than that of the composite magnetic particle. Theelectromagnetic wave absorber has a good electromagnetic wave absorptioncharacteristic in the high frequency region, particularly, in GHzregion, and can be formed in a thin electromagnetic wave absorber, andcan efficiently suppress electromagnetic wave interference insideelectronic equipment.

BRIEF DESCRIPTION OF DRAWINGS

[0064]FIG. 1 is a microscopic photograph (TEM photograph) showing across section of an Fe-SiO₂ magnetic composite grains in accordance withthe present invention.

[0065]FIG. 2 is a graph showing a measured result of the frequencycharacteristics of the magnetic permeability of magnetic compositegrains in accordance with the present invention and the magneticpermeability of a comparative mixed powder.

[0066]FIG. 3 is a graph showing a measured result of the frequencycharacteristics of the dielectric constant of the magnetic compositegrains in accordance with the present invention and the dielectricconstant of the comparative mixed powder.

[0067]FIG. 4 is a graph showing a measured result of the frequencycharacteristics of reflectivity of the magnetic composite grains inaccordance with the present invention and the reflectivity of thecomparative mixed powder.

[0068]FIG. 5 is a photograph of high resolution transmission electronmicroscope showing a cross section of a composite magnetic particle inaccordance with the present invention.

[0069]FIG. 6 is a graph showing the frequency characteristic of thecomplex specific magnetic permeability of a composite magnetic particlein which the magnetic metal phase and the ceramic phase are unified innano-meter level.

[0070]FIG. 7 is a graph showing the frequency characteristic of thecomplex specific dielectric constant of the composite magnetic particlein which the magnetic metal phase and the ceramic phase are unified innano-meter level.

[0071]FIG. 8 is a graph showing the electromagnetic wave absorptioncharacteristic of the composite magnetic particle in which the magneticmetal phase and the ceramic phase are unified in nano-meter level.

[0072]FIG. 9 is a cross-sectional view showing an electromagnetic waveabsorber in which oblate composite magnetic particles are oriented in aresin.

[0073]FIG. 10 is a cross-sectional view showing a semiconductorintegrated element which is molded in a package with a sealing resinmixed with the composite magnetic particles.

[0074]FIG. 11 is a cross-sectional view showing a printed wiring boardhaving an electromagnetic wave absorption layer formed of theelectromagnetic wave absorber in accordance with the present invention.

[0075]FIG. 12 is a cross-sectional view showing an electromagnetic waveabsorption cap arranged on a printed wiring board so as to enclose asemiconductor element of a noise source.

[0076]FIG. 13 is a cross-sectional view showing an electronic equipmentcasing formed of the electromagnetic wave absorber in accordance withthe present invention.

[0077]FIG. 14 is a cross-sectional view showing an optical sendingmodule which is completely sealed with a resin mixture containing thecomposite magnetic particles, and the outside is further covered with ametal casing.

[0078]FIG. 15 is a cross-sectional view showing the optical sendingmodule of which the metal casing is removed.

[0079]FIG. 16 is a cross-sectional view showing an optical sendingmodule of two-layer structure in which only the wiring portion is sealedwith an insulation resin not containing the composite magneticparticles, and the outside of the insulation resin is sealed with aresin mixture containing the composite magnetic particles.

[0080]FIG. 17 is a plan view showing a first form of an optical sendingand receiving module of the optical sending and receiving module.

[0081]FIG. 18 is a cross-sectional view showing the construction of atollgate using an electronic toll collection system (ETC) in which theelectromagnetic wave absorber in accordance with the present inventionis arranged in the ceiling surface of the gate roof and columns.

[0082]FIG. 19 is a cross-sectional view showing an electromagnetic waveabsorber having a multi-layer structure in accordance with the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0083] (Embodiment 1)

[0084] A mixed powder of Fe powder of 50 vole % having grain size of 1to 5 μm and SiO₂ powder of 50 vole % having an average grain size of 0.3μm, and balls made of SUS410 (diameter: 9.5 mm) with a weight ratio ofthe powders to the balls=1 to 80 were put into a pot made of stainlesssteel together, and the pot was filled with argon gas, and MA(mechanical alloying) treatment was performed with rotation speed of 200rpm for 100 hours. The composite magnetic particles after the MA was ofindefinite shape having complicated shapes, and the average particlesize was several tens μm.

[0085]FIG. 1 is a TEM photograph of the structure obtained fromobservation of the composite magnetic particle using a TEM. The crystalgrain size of Fe of the black portion in the photograph is 10 nm, andthe composite magnetic particle has a complicated shape, and Si oxide ofthe white portion is formed in a network-shape so as to enclose Fegrains having grain size below 100 nm. The fine Fe grains having grainsize below 20 nm were independently formed, and the complicated shapedFe grains having grain size larger than the grain size of the fine grainwere formed by gathering the fine grains. Further, the Si oxide wasdispersed in the Fe crystal grain boundaries, and the Fe grains and theSi oxide were alternatively formed in an oblate shape. Further, the Sioxide was also formed in a bar-shape, and Si oxide grains having adiameter below 0.05 gm and a length of 0.2 to 0.5 μm were formed with adensity of 10 to 20 in number per 1 μm square.

[0086] Further, after MA, annealing of the composite magnetic particleswas performed in a vacuum (the degree of vacuum: above 10⁻⁶ Torr) attemperature of 500° C. for 1 hour. After that, the composite magneticparticles of 50% in volume ratio to epoxy resin were kneaded with theepoxy resin, and was press-formed into a tablet shape, and then thetablets were cured by uniaxially pressing with 210 kgf at 180° C. Afterthat, the cured tablets were finished in a toroidal shape of 7-0.05 mmouter diameter, 3.04+0.06 mm inner diameter, 2 mm and 4 mm thickness.

[0087] When a complex specific dielectric constant and a complexspecific magnetic permeability of the sample were measured using ameasurement system composed of a network analyzer (a product of HP:8720C) and a coaxial waveguide, after calibrating so that the magneticpermeability and the dielectric constant of the free space might become1, the sample was inserted into the coaxial waveguide to measure twoparameters S11 and S21 using two ports, and then the complex specificdielectric constant and the complex specific magnetic permeability werecalculated from the measured parameters.

[0088] Further, when a reflection characteristic was measured, aftercalibrating so that the reflection coefficient of the free space mightbecome 0, the sample was inserted into the coaxial waveguide to measurea parameter S11, and then the reflection coefficient of the sample wascalculated from the measured parameter. The range of measured frequencywas 50 MHz to 20 GHz.

[0089] In order to investigate the effect of the composite magneticparticles in which the insulation metal oxide particle were dispersed ina soft magnetic metal particle, measurements of complex specificmagnetic permeability, complex specific dielectric constant andfrequency characteristics of reflection coefficient were performed usingthe Fe-50vole % SiO₂ manufactured through the method of the presentinvention and a sample which was manufactured by performing mechanicalmilling treatment of Fe powder and SiO₂ powder separately under the samecondition as that of the MA treatment and then annealing the powders,and after that, simply mixing the two annealed powders using a V-mixerand then forming the composite structure with epoxy resin. The comparingresults are shown in FIG. 2 to FIG. 4.

[0090] It can be understood from FIG. 2 that both of the real part andthe imaginary part of the complex specific magnetic permeability for thecomposite magnetic particle sample in the high frequency region arehigher than those for the sample of simply mixing the Fe powder and theSiO₂ powder using the V-mixer.

[0091] It can be understood from FIG. 3 that both of the real part andthe imaginary part of the complex specific dielectric constant for thecomposite magnetic particle sample is slightly decreased due to thecomposite structure, and accordingly it is easy to adjust the impedancematching with the free space.

[0092]FIG. 4 shows the frequency characteristics of the reflectioncoefficients in a case of the sample thickness of 108 mm. The reflectioncoefficient for the composite magnetic particle sample is smaller, andthe central frequency (a frequency where the reflection coefficientbecomes minimum) for the composite magnetic particle sample exists inthe lower frequency side. Further, the frequency band width satisfyingthe reflection coefficient below −10 dB is wider in the compositemagnetic particle sample.

[0093] It can be understood from the above results that theelectromagnetic absorption characteristic for the composite magneticparticle unified the soft magnetic metal powder and the insulation metaloxide in the nano-meter scale is improved compared with that for thesample of simply mixing the two kinds of powders.

[0094] (Embodiment 2)

[0095] A mixed powder of Fe powder having grain size of 1 to 5 μm andsoft magnetic metal oxide powder of (Ni—Zn—Cu)Fe₂O₄ or (Mn—Zn)Fe₂O₄(50:50 in volume ratio) having an average grain size of 0.7 μm, andballs made of SUS410 (diameter: 9.5 mm) with a weight ratio of thepowders to the balls=1 to 80 were put into a pot made of stainless steeltogether, and the pot was filled with argon gas, and MA (mechanicalalloying) treatment was performed with rotation speed of 200 rpm for 100hours. The composite magnetic particles after the MA was of indefiniteshape, and the average particle size was several tens am. Further, theresult of observing the composite magnetic particle using the TEM wassimilar to that of Embodiment 1. The crystal grain size of Fe was about10 nm, and oxides including components of the soft magnetic metal oxidewere finely dispersed in a network shape in the crystal grain boundary.Annealing of the composite magnetic particles was performed in a vacuum(the degree of vacuum: above 10⁻⁶ Torr) at temperature of 500° C. for 1hour. The composite magnetic particle showed the structure similar tothat of Embodiment 1.

[0096] In order to investigate the effect of the composite magneticparticles, measurements of various characteristics were performed usingthe composite magnetic particles according to the present invention anda sample which was manufactured by performing mechanical millingtreatment of Fe powder and soft magnetic metal oxide powder separatelyunder the same condition as that of the MA treatment and then annealingthe powders, and after that, simply mixing the two annealed powdersusing a V-mixer and then forming the composite structure with epoxyresin. As the results of comparison, the effect similar to that ofEmbodiment 1 was obtained.

[0097] (Embodiment 3)

[0098] A powder of mixing Fe powder having grain size of 1 to 5 μm andSi powder having an average grain size of 1.0 μm of 50:50 in volumeratio, and the same balls made of SUS410 as described above with aweight ratio of the powders to the balls=1 to 80 were put into a potmade of stainless steel together, and the pot was filled with oxygen gas(Ar:O₂=4:1), and mechanical alloying (MA) treatment was performed withrotation speed of 200 rpm for 100 hours. The composite powder after theMA was of indefinite shape, and the average particle size was 5.0 μm.Further, as the result of observing the composite magnetic particleusing the TEM, the crystal grain size of Fe was about 10 nm, and oxidesincluding components of Si oxide was finely dispersed in a network shapein the crystal grain boundary. Further, as a result of an X-raydiffraction analysis, it was checked that there were Fe oxides (Fe₂O₃,Fe₃O₄). Similarly to the method described above, various kinds ofcharacteristics of the composite magnetic particles mixed with epoxyresin were measured. As the result, the structure and thecharacteristics similar to those of the composite magnetic particlesmanufacture through the method of Embodiment 1 were obtained.

[0099] (Embodiment 4)

[0100] The particle surfaces of the composite magnetic particlesobtained from Embodiments 1 to 3 were coated with a non-magnetic ormagnetic oxide having a high electric resistivity. The coating methodused was a surface oxidation method or a mechanical composition method.

[0101] By setting the atmospheric condition at annealing in themanufacturing process of the composite magnetic particles to theatmosphere or an oxygen atmosphere as the surface oxidation method, itwas checked from an X-ray diffraction analysis that oxides such as Fe₃O₄were produced.

[0102] On the other hand, a mechano-fusion method using a kind ofshearing type mill was employed as the mechanical composition method. Indetail, the composite magnetic particles (average particle size: 10 μm)were used as the host particles, and SiO₂ (average particle size: 0.016μm) or (Ni—Zn—Cu)Fe₂O₄ (average particle size: 0.5 μm) were used as theguest particles. The host particles and the guest particles were mixedin the volume ratio of 2:3, and then put into the mechano-fusionapparatus. The conditions of mechano-fusion were in a vacuum, rotatingspeed: 1000 rpm, and treatment time: 3 hours. As the result, it waschecked from SEM observation that the surfaces of the composite magneticparticles were coated with relatively compact oxide film of about 1.0 μmthickness formed of the guest particles.

[0103] (Embodiment 5)

[0104] A mixed powder of Fe powder of 70 vole % having grain size of 1to 5 μm and SiO₂ powder of 30 vole % having an average grain size of 0.3μm, and balls made of stainless steel were put into a pot made ofstainless steel together, and the pot was filled with argon gas, andmechanical alloying treatment was performed. The composite magneticparticles after the mechanical alloying was of indefinite shape, and theaverage particle size was several tens μm. After that, annealing of thecomposite magnetic particles was performed in a vacuum (the degree ofvacuum: above 10⁻⁶ Torr) at temperature of 500° C. for 1 hour.

[0105] The method of unifying the fine crystal grains of the magneticmetal (hereinafter, referred to as magnetic metal grains) and theceramic grains is not limited to the mechanical alloying methoddescribed above. For example, the following methods are applicable. Thatis a method that an alloy powder, which is composed of a magnetic metaland an element having an affinity with oxygen, nitrogen and carbonhigher than the magnetic metal and has a high content of any one ofthese gas elements, is fabricated through the atomizing method, and thenthe soft magnetic metal phase and the ceramic phase are separatelyproduced by performing heat treatment of the alloy powder; and a methodthat an alloy powder, which is composed of a magnetic metal and anelement having an affinity with oxygen, nitrogen and carbon higher thanthe magnetic metal and has a high content of any one of these gaselements, is fabricated through the atomizing method, and then heattreatment of the alloy powder is performed in a gas atmospherecontaining any one of oxygen, nitrogen and carbon; and a method that thesoft magnetic metal phase and the ceramic phase are separately produced;and a sol-gel method using metal alkoxide. The manufacturing method isnot limited to the above-described methods, but a manufacturing methodcapable of finally obtaining the composite magnetic particles composedof the magnetic metal grain phase and the high electric resistivityceramic phase.

[0106] In order to increase the electric resistivity of the compositemagnetic particle itself, it is possible that a high electricresistivity film such as an oxide film or a nitride film is formed onthe surface of the composite magnetic particle at the same timeproducing the composite magnetic particles.

[0107] Further, it is possible to coat the surface of the compositemagnetic particle with a material having a higher electric resistivitythrough a mechanical unifying method, preferably through themechano-fusion method using a kind of shearing type mill. In detail, thecomposite magnetic particles (average particle size: 10 μm) were used asthe host particles, and SiO₂ (average particle size: 0.016 am) or(Ni—Zn—Cu)Fe₂O₄ (average particle size: 0.5 μm) were used as the guestparticles. The host particles and the guest particles were mixed in thevolume ratio of 2:3, and then put into the mechano-fusion apparatus(preferably in a vacuum, rotating speed: 1000 rpm, and treatment time: 3hours). As the result, it was checked from SEM observation that thesurfaces of the composite magnetic particles were coated with relativelycompact oxide film of about 1.0 μm thickness formed of the guestparticles.

[0108]FIG. 5 is a TEM photograph of the composite magnetic particleannealed under a vacuum after the mechanical alloying treatment. Theblack portion in the photograph was fine crystal grains of Fe, and thecrystal grain size was 10 to 20 nm. Amorphous Si oxide existed so as toenclose the fine crystal grains of Fe.

[0109] Then, after drying and crushing treatment, the composite magneticparticles were press-formed into a tablet shape under room temperature.Further, the tablets were cured by uniaxially pressing with 210 kgf at180° C. Therein, as the other methods of manufacturing the resincomposite body, there are the injection molding method, the transfermold method and so on. When a sheet-shaped resin composite body ismanufactured, the doctor blade method, the spin coat method, thecalendar roll method are applicable.

[0110] These resin composite bodies were finished in a toroidal shape of7-0.05 mm outer diameter, 3.04+0.06 mm inner diameter, 0.5 to 2 mmthickness by machining and grinding. Next, in regard to thecharacteristic evaluation method, when a complex specific dielectricconstant and a complex specific magnetic permeability of the sample weremeasured using a measurement system composed of a network analyzer (aproduct of HP: 8720C) and a coaxial waveguide, after calibrating so thatthe magnetic permeability and the dielectric constant of the free spacemight become 1, the sample was inserted into the coaxial waveguide tomeasure two parameters S11 and S21 using two ports, and then the complexspecific dielectric constant and the complex specific magneticpermeability were calculated using Nicolson-Ross, Weir method from themeasured parameters.

[0111] Further, when a reflection characteristic was measured, aftercalibrating so that the reflection coefficient of the free space mightbecome 0, the sample was inserted into the coaxial waveguide to measurea parameter S11, and then the reflection coefficient of the sample wascalculated from the measured parameter. The range of measured frequencywas 0.1 to 18 GHz.

[0112] In order to compare the characteristics of the composite magneticparticles with those of single phase Fe particles, a sample wasmanufactured by separately performing mechanical milling treatment of Fepowder having grain size of 1 to 5 μm and SiO₂ powder having an averagegrain size of 0.3 μm under the same condition as that of the mechanicalalloying treatment, putting the Fe powder and the SiO₂ powder of thevolume ratio of 70:30 together, and sufficiently mixing using a V-mixer,and then forming the mixed powder annealed in the same condition asdescribed above into the composite structure with epoxy resin throughthe same method as described above. The complex specific magneticpermeability, the complex specific dielectric constant and the frequencycharacteristics of reflection coefficient of the sample were measured.

[0113]FIG. 6 to FIG. 8 show comparison of the complex specific magneticpermeability, the complex specific dielectric constant and the frequencycharacteristics of reflection coefficient between the composite magneticparticles and the single phase Fe particles. It can be understood fromFIG. 5 that both of the real part and the imaginary part of the complexspecific magnetic permeability in the high frequency region for thecomposite magnetic particle sample are higher than those for the simplemixed powder of the Fe powder and the SiO₂ powder. It can be understoodfrom FIG. 7 that the real part of the complex specific dielectricconstant for the composite magnetic particles is larger than that of thesimple mixed powder, and the imaginary part for the composite magneticparticles is also slightly increased. FIG. 8(a) shows the frequencycharacteristic of reflection coefficient in a case where there is ametal plate on the one side of the electromagnetic wave absorber, andthe reflection coefficient for the composite magnetic particle issmaller. FIG. 8(b) shows the measured results of an amount ofelectromagnetic wave absorption of the electromagnetic wave absorberitself, and the amount of electromagnetic wave absorption for thecomposite magnetic particle is larger.

[0114] It can be understood from the above results that theelectromagnetic absorption characteristic can be improved by unifyingthe soft magnetic metal grain phase and the high electric resistivityceramic phase in the nano-meter scale.

[0115] (Embodiment 6)

[0116] In Embodiment 5, in cases where an alloy containing Ni, Coinstead of Fe or containing at least one ferromagnetic metal among thesemetals, for example, parmalloy of Fe—Ni group, sendust of Fe—Al—Sigroup, Fe—Ni alloy group, Fe—Cr alloy group, Fe—Cr—Al alloy group wereused, and in cases where alumina (Al₂O₃), Mn—Zn group ferrite, Ni—Zngroup ferrite of spinel group as a magnetic oxide, in addition, plannartype hexagonal ferrite, magneto-planbite type ferrite were used insteadof SiO₂, the same effect could be obtained.

[0117] (Embodiment 7)

[0118] In order to make the shape of the composite magnetic particlesafter mechanical alloying treatment in Embodiment 5 or 6 oblate, oblatecomposite magnetic particles having an aspect ratio above 2 wereobtained by putting the composite magnetic particles into a crasher suchas a planetary ball mill (or an attriter) together with an organicsolvent such as ethanol to perform wet treatment. After heat treatment,the oblate composite magnetic particles were mixed with a liquid resinto make a paste state, and formed in a sheet-shape through thedoctor-blade method in which shear force is applied to the compositemagnetic particles, and then press-formed using a hot press. As theresult of observing a cross section of the sheet using a SEM, the oblatecomposite magnetic particles were orientated, as shown in FIG. 9.

[0119] A composite compound of the oblate composite magnetic particlesand a resin was manufactured in advance, and then injected to a metalmold using an injection molding machine. As the result of observing across section of the molded piece using the SEM, the oblate compositemagnetic particles were highly orientated, as shown in FIG. 9. In thecase where the oblate composite magnetic particles are highly orientedin the resin, it was observed that the real parts of the complexspecific magnetic permeability and the complex specific dielectricconstant were improved compared to those in Embodiments 5 and 6, and theelectromagnetic wave absorptivity was largely improved.

[0120] (Embodiment 8)

[0121]FIG. 10 is a cross-sectional view showing a semiconductorintegrated device which is sealed with a sealing resin mixed with thecomposite magnetic particles described in Embodiments 1 to 7. As shownin FIG. 10, by molding packages with a sealing resin mixed with thecomposite magnetic particles in a manufacturing process ofmicroprocessors or LSIs, electromagnetic wave generated from ICs and aninner leads composing the semiconductor integrated element is absorbedto suppress the internal interference. By covering the semiconductorelement side of the sealing resin mixed with the composite magneticparticles with a resin of composite magnetic particle free, it ispossible to prevent electric contact with the lead. Electric connectionbetween the ICs and the externals is performed by solder balls 7 throughthe printed wiring board 9. The leads 8 are made of any one of Au, Cu orAl wire.

[0122] (Embodiment 9)

[0123]FIG. 11 is a cross-sectional view showing a printed wiring boardhaving an electromagnetic wave absorption layer formed of theelectromagnetic wave absorber described in Embodiments 1 to 7. In aprinted wiring board having a wiring circuit 13 in an insulation board9, a paint comprising the electromagnetic wave absorber composed of thecomposite magnetic particles and a material having an electricresistivity higher than that of the composite magnetic particle isdirectly applied or a film formed the paint into a sheet-shape isattached onto a part or the whole of an insulation layer 10 on thesurface of the insulation board 9 having a wiring circuit 13 formedthereon and the opposite surface of the insulation board 9 not havingthe wiring circuit to form an electromagnetic wave absorption layer.Thereby, occurrence of noises such as a cross-talk phenomenon due toelectromagnetic wave generated from the printed wiring circuit board canbe suppressed. Further, by arranging a conductive layer outside each ofthe electromagnetic wave absorption layers, the electromagnetic waveabsorptivity can be improved, and the shielding effect toelectromagnetic wave from the outside can be improved.

[0124] (Embodiment 10)

[0125]FIG. 12 is a cross-sectional view showing an electromagnetic waveabsorption cap arranged on a printed wiring board so as to enclose asemiconductor element of a noise source. The electromagnetic waveabsorption cap in accordance with the present invention is arranged on aprinted wiring board so as to enclose semiconductor elements of noisesources such as a microprocessor, a system LSI etc. FIG. 12(a) is a casewhere the electromagnetic wave absorption layer in accordance with thepresent invention is arranged on the inner surface of the metal cap, andelectromagnetic wave from the outside can be shielded andelectromagnetic wave emitted from the inside can be absorbed. FIG. 12(b)is a case where a cap molded by injection molding of the electromagneticwave absorber in accordance with the present invention is used. Bymounting the cap, the electromagnetic wave emitted from thesemiconductor element can be efficiently absorbed to suppress theinternal interference.

[0126] (Embodiment 11)

[0127]FIG. 13 is a cross-sectional view showing an electronic equipmentcasing formed of the electromagnetic wave absorber in accordance withthe present invention. FIG. 13(a) is a case where the electromagneticwave absorption layer in accordance with the present invention isapplied onto the inner surface of a metal casing for electronicequipment or the electromagnetic wave absorption layer formed throughinjection molding is arranged on the inner surface. FIG. 13(b) is a casewhere the electronic equipment casing is molded by injection molding ofthe electromagnetic wave absorber in accordance with the presentinvention. By adding the function of absorbing electromagnetic wave tothe electronic equipment casing as described above, electromagnetic waveinterference inside the electronic device can be suppressed.

[0128] (Embodiment 12)

[0129]FIG. 14 is a view showing the construction of an optical sendingmodule in accordance with the present invention. The optical sendingmodule 21 comprises an optical fiber 25, an optical guide path 29, an LD26, a sending circuit 27, a circuit board 28 etc. The sending circuit 27is composed of an LD driver for driving the LD 26 of a laser diode, alaser output control part, a flip-flop circuit and so on. Actually,there are a lead frame, wiring and so on, but there are not shown in thefigure. In the present embodiment, the optical sending module isperfectly sealed by putting it into a mold, by pouring the resin mixturecontaining the composite magnetic particles described Embodiments 1 to 7into the mold, and by curing the resin mixture. Further, the outside ofthe molded optical sending module is covered with a metal casing 30. Bydoing so, the elements and the board can be protected from water andgas, and at the same time electromagnetic wave can be absorbed andshielded to suppress noise interference inside the sending module, andemission of electromagnetic wave outside the module can be completelyprevented.

[0130] The meal casing 30 is not always necessary. Therefore, as shownin FIG. 15, the module may be only sealed with the resin mixture. Thisstructure is inferior to the above case covered with the metal casing inabsorption and shielding effects of electromagnetic wave, but has anadvantage of low cost.

[0131] Further, short circuiting between the wires can be prevented bycoating the surfaces of the composite magnetic particles withinsulation. As the method of coating insulation, there are a method thata film having an electric resistivity such as an oxide film or a nitridefilm is formed on the surface of the composite magnetic particle by heattreatment in an atmosphere; a chemical film forming method using acoupling treatment agent of silane group, alkylate group or titanategroup, or a magnesium phosphate-borate insulation treatment agent; and amechanical film forming method that the surface of the compositemagnetic particle is coated with a material having a higher electricresistivity through the mechano-fusion method using a kind of shearingtype mill.

[0132] Further, a more reliable method of preventing short circuitingbetween the wires is a two-layer structure that only the wiring portionsare sealed with an insulating resin not containing the compositemagnetic particles, and then sealed thereon with the resin mixturecontaining the composite magnetic particles, as shown in FIG. 16.

[0133] The particle size of the composite magnetic particle ispreferably below 40 μm in taking the fluidity of the resin mixture intoconsideration though the size depends on the composition of thecomposite magnetic particle. The shape of the composite magneticparticle may be spherical or oblate. The filling amount of the compositemagnetic particles to the resin is preferably below 60 vole % from theviewpoint of securing the fluidity of the resin mixture. The usableresin, in addition to epoxy group resin commonly used as sealing resinof electronic equipment, are polyester group resins; polyvinyl chloridegroup resins; polyvinyl butylal resin; polyurethane resin; cellulosegroup resins; copolymer of these resins; epoxy resin; phenol resin;amide group resins; imide group resins; nylon; acrylic resin; syntheticrubber; and so on.

[0134] Although the present embodiment has been described on the LD 26and the sending circuit 27, an optical receiving module may be similarlyconstructed by replacing these by PD and receiving circuit.

[0135] (Embodiment 13)

[0136]FIG. 17 is a plan view showing a first form of an optical sendingand receiving module of the optical sending and receiving module. Theoptical sending and receiving module 23 comprises a function both of theoptical sending module and the optical receiving module described above.The optical sending portion comprises an optical fiber 25, an opticalguide path 29, an LD 26, a sending circuit 27, a circuit board 28 and soon. The sending circuit comprises an LD driver for driving a laser, alaser output control portion, a flip-flop circuit and so on. The opticalreceiving portion comprises an optical fiber 25, an optical guide path29, a PD 35, a receiving circuit 36, a circuit board 28 and so on. Thereceiving circuit comprises a PRE IC having a pre-amplifying function, aCDR LSI composed of a clock extraction portion and an equivalentamplifier, an SAW of a narrow band filter, an APD bias control circuitand so on. Actually, there are a lead frame, wiring and so on, but thereare not shown in the figure.

[0137] In the sending and receiving module integrating the sendingmodule and the receiving module, the internal noise interference due tonoise sending and receiving between the optical sending portion and theoptical receiving portion particularly becomes a problem, as describedabove.

[0138] In the present embodiment, the arrangement of the electromagneticwave absorber can be constructed similarly to that of Embodiment 12, asshown in FIG. 14 to FIG. 16.

[0139] In a conventional optical sending and receiving module, noiseinterference is prevented by arranging a shield plate made of a metalbetween the sending portion and the receiving portion, or by containingeach of the modules into a package made of a metal to form a separatesending module and a separate receiving module. However, such a modulehas problems that the whole module becomes large in size and heavy inweight, and in addition the cost can not be lowered because of use ofthe high cost metal package. By employing the structure of the presentinvention, the noise interference inside the module can be prevented,and the module can be made small in size, light in weigh and low incost.

[0140] Further, according to the present embodiment, it is possible toprovide an optical sending module, an optical receiving module or anoptical sending and receiving module having both of an optical sendingportion and an optical receiving portion which are capable of being usedin a high speed communication network, and can suppress internal noiseinterference and noise emission to the outside, and can be made small insize, light in weight, high in processing speed and high in sensitivity.

[0141] (Embodiment 14)

[0142]FIG. 18 is a cross-sectional view showing the construction of atollgate to which an electronic toll collection system (hereinafter,referred to as ETC). The ETC is capable of sending and receivinginformation between a road side communication unit and an in-car unitmounted on a vehicle passing through the tollgate.

[0143] As shown in FIG. 18, electromagnetic wave of frequency of 5.8 GHZis used among an entrance portion antenna 40, an exit portion antenna 41and the in-car unit 41 to exchange information necessary for paying andreceiving toll. The spread of the electromagnetic wave sent from theexit portion antenna 41 (direct wave 46) becomes wider due to anelectromagnetic wave multi-reflection phenomenon with the road surface43 and the ceiling 44 of the gate roof 43 or columns 45. Thereby, asshown in FIG. 18, it can be predicted to cause an erroneous operationdue to electromagnetic wave disturbance such as a problem ofinterference to a vehicle in the adjacent lane and a problem ofdistinction between vehicles that the electromagnetic wave sent from theexit portion antenna 41 (direct wave 46) is sent to the in-car unit ofthe vehicle A48, and at the same time the reflected wave 47 reflected bythe roar surface 43 is sent to an in-car unit 42 of the followingvehicle B48. Therefore, the above problem can be solved by arranging theelectromagnetic wave absorbers containing the composite magneticparticles in the ceiling surface of the gate roof 44 and the columns toabsorb the reflected wave.

[0144] A conventional electromagnetic wave absorber for ETC is of anintegrated type, and the thickness is as thick as several tens cm.Therefore, it is difficult to attach it onto a portion having a complexshape. Accordingly, development of an electromagnetic wave absorber of apaint type or a soft and thin is required. The electromagnetic waveabsorber 49 is made of the resin mixture containing the compositemagnetic particles, and can be formed into a paint type or a soft sheettype depending on selection of the resin. Further, the compositemagnetic particles are excellent particularly in the electromagneticwave characteristics in the high frequency region above 5 GHz comparedto the conventional soft magnetic metal particles. Therefore, theseproblems can be solved by the electromagnetic wave absorber inaccordance with the present invention.

[0145] The electromagnetic wave absorber 49 using resin mixturecontaining the composite magnetic particles may be formed in a singlelayer structure. However, in order to improve the oblique incidentcharacteristic, it is more effective to be formed in a multi-layerstructure in which the impedance of the electromagnetic wave absorber tothe incident wave 50 is gradually decreased from the wave incidentsurface toward the side of the metal layer of perfect reflector. Indetail, the complex specific magnetic permeability and the complexspecific dielectric constant are gradually decreased from the waveincident surface toward the side of the metal layer 51. In order to doso, the filling amount of the composite magnetic particles of the samecomposition to the resin is varied, or the composition of the compositemagnetic particles in the resin is varied. Therein, the metal layer isnot necessary when the attached surface is made of a metal. In FIG. 19,the electromagnetic wave absorber 49 is composed of three layers.

[0146] The particle size of the composite magnetic particle ispreferably below 40 μm in taking the fluidity of the resin mixture intoconsideration though the size depends on the composition of thecomposite magnetic particle. The shape of the composite magneticparticle may be spherical or oblate, and particularly not limited. Thefilling amount of the composite magnetic particles to the resin for eachlayer is preferably 60 vole % at maximum from the viewpoint of securingthe fluidity of the resin mixture. The usable resin may be anyinsulation polymer, and the resins described in Embodiment 12 arepreferable.

What is claimed is:
 1. An electromagnetic wave absorber comprisingcomposite magnetic particles having a grain size smaller than 10 μm inwhich magnetic metal grains and ceramic are unified.
 2. Anelectromagnetic wave absorber comprising composite magnetic particles inwhich a plurality of fine magnetic metal grains and ceramic are unifiedby enclosing said plurality of fine magnetic metal grains with saidceramic.
 3. An electromagnetic wave absorber comprising compositemagnetic particles in which magnetic metal grains and a plurality ofceramic grains are unified by embedding the ceramic grains into themagnetic metal grains.
 4. An electromagnetic wave absorber according toany one of claim 1 to claim 3, wherein said magnetic metal is at leastone kind of metal or alloy selected from the group consisting of iron,cobalt and nickel, and said ceramic is at least one kind of ceramicselected from the group consisting of oxide, nitride and carbide ofiron, aluminum, silicon, titanium, barium, manganese, zinc, magnesium,cobalt and nickel.
 5. An electromagnetic wave absorber according to anyone of claim 1 to claim 4, wherein the magnetic metal grain and ceramicare unified by bonding the ceramic onto the surface of the compositemagnetic particle.
 6. An electromagnetic wave absorber according to anyone of claim 1 to claim 5, wherein said composite magnetic particleshave an average crystal grain size smaller than 50 nm.
 7. Anelectromagnetic wave absorber, wherein said composite magnetic particlesdescribed in any one of claim 1 to claim 6 are dispersed in a materialhaving an electric resistivity higher than an electric resistivity ofsaid composite magnetic particles.
 8. An electromagnetic wave absorberaccording to claim 7, wherein said material having a high electricresistivity is any one of a resin, an insulation polymer paint and aceramic sintered material.
 9. A method of manufacturing anelectromagnetic wave absorber, wherein composite magnetic particles, inwhich magnetic metal grains and ceramic are unified, are formed througha mechanical alloying method of a magnetic metal powder and a ceramicpowder.
 10. A method of manufacturing an electromagnetic wave absorber,wherein composite magnetic particles, in which magnetic metal grains andceramic are mixed and unified, are formed by a mechanical alloyingmethod of a composite powder containing a magnetic metal powder and aceramic powder using metallic balls or ceramic balls, size of said ballbeing larger than grain size of the metallic powder, a volumetric amountof said balls being larger than a volumetric amount of said compositepowder.
 11. A composite member comprising composite magnetic particlesin which magnetic metal particles and ceramic are unified.
 12. Acomposite member formed by compounding composite magnetic particles, inwhich magnetic metal grains and ceramics are unified, and a materialhaving an electric resistivity higher than an electric resistivity ofthe composite magnetic particle.
 13. A electromagnetic wave absorberformed by compounding composite magnetic particles, in which magneticmetal grains and ceramics are unified, and at least one kind of materialselected from the group consisting of a resin having an electricresistivity higher than an electric resistivity of the compositemagnetic particle alumina and silica.
 14. A electromagnetic waveabsorber according to any one of claims 1 to 8, 12 and 13, wherein avolume ratio of said ceramic to the composite magnetic particle is 10 to75%, and said ceramic is embedded in said magnetic metal grains.
 15. Aelectromagnetic wave absorber according to any one of claims 1 to 8 and12 to 14, wherein an average crystal grain size of said compositemagnetic particle is smaller than 50 nm.
 16. A electromagnetic waveabsorber according to any one of claims 1 to 8 and 12 to 15, wherein thesurface of said composite magnetic particle is coated with a materialhaving an electric resistivity higher than an electric resistivity ofsaid composite magnetic particle.
 17. A electromagnetic wave absorberaccording to any one of claims 1 to 8 and 12 to 16, wherein saidcomposite magnetic particle has an aspect ratio larger than 2, and hasan oblate shape.
 18. A electromagnetic wave absorber according to anyone of claims 1 to 8 and 12 to 17, wherein said composite magneticparticles are uniformly dispersed in said material having the highelectric resistivity.
 19. A electromagnetic wave absorber according toany one of claims 1 to 8 and 12 to 18, wherein said oblate compositemagnetic particles are oriented in one direction in said material havingthe high electric resistivity.
 20. A electromagnetic wave absorberaccording to any one of claims 12 to 19, wherein said material havingthe high electric resistivity is a polymer material or a ceramicsintered material.
 21. A semiconductor device in which a semiconductorelement mounted on a printed wiring board is sealed with a resincontaining an electromagnetic wave absorber, wherein said resin in theside of said element is covered with a resin free from saidelectromagnetic wave absorber.
 22. A printed wiring board comprising awiring circuit on an insulation board, and said circuit is covered withan insulation layer, wherein layers comprising an electromagnetic waveabsorber are formed on a surface of said insulation board opposite tothe surface having said wiring circuit formed and on said insulationlayer.
 23. A semiconductor device, wherein a semiconductor elementmounted on a printed wiring board is covered with a metal cap of whichan inner peripheral surface is formed of an electromagnetic waveabsorber.
 24. A semiconductor device, wherein a semiconductor elementmounted on a printed wiring board is covered with a cap having anelectromagnetic wave absorber.
 25. A semiconductor device, wherein aprinted wiring board and a semiconductor element mounted on said boardare covered with a casing having an electromagnetic wave absorber.
 26. Asemiconductor device, wherein a printed wiring board and a semiconductorelement mounted on said board are covered with a metal casing of whichan inner peripheral surface is formed of an electromagnetic waveabsorber.
 27. An optical sending or receiving module comprising at leastone of a light emitting element and a light receiving element; and atleast one of a sending circuit and a receiving circuit on a circuitboard, wherein said circuit board, said element and said circuit arecovered with a member having an electromagnetic wave absorber.
 28. Anoptical sending or receiving module comprising at least one of a lightemitting element and a light receiving element; and at least one of asending circuit and a receiving circuit on a circuit board, wherein saidcircuit board, said element and said circuit are covered with a metalcap of which an inner peripheral surface is covered with a member havingan electromagnetic wave absorber.
 29. An optical sending or receivingmodule comprising at least one of a light emitting element and a lightreceiving element; and at least one of a sending circuit and a receivingcircuit on a circuit board, wherein said circuit board, said element andsaid circuit are covered with a member having an electromagnetic waveabsorber, and an outer peripheral surface of said member is covered witha metal cap.
 30. An optical sending or receiving module according to anyone of claims 27 to 29, wherein said circuit board, said element andsaid circuit are covered with insulation resin.
 31. An automatictollgate comprising a tollgate roof; an entrance portion antennaarranged in an entrance side to a vehicle passing through the tollgate;an exit portion antenna arranged in an exit side to the vehicle passingthrough the tollgate; an electronic toll collection system for sendingand receiving information between a road-side communication unit and anin-car unit mounted on said vehicle, wherein an electromagnetic waveabsorber comprising magnetic metal particles and ceramic is formed on asurface of said gate roof in the running side of said vehicle, andsurfaces of columns for supporting the entrance portion antenna and theexit portion antenna.
 32. An automatic tollgate comprising a tollgateroof; an entrance portion antenna arranged in an entrance side to avehicle passing through the tollgate; an exit portion antenna arrangedin an exit side to the vehicle passing through the tollgate; anelectronic toll collection system for sending and receiving informationbetween a road-side communication unit and an in-car unit mounted onsaid vehicle, wherein an electromagnetic wave absorber compoundedcomposite magnetic particles having magnetic metal grains and ceramicsand a material having an electric resistivity higher than an electricresistivity of said composite magnetic particle is formed on a surfaceof said gate roof in the running side of said vehicle, and surfaces ofcolumns for supporting the entrance portion antenna and the exit portionantenna.
 33. An automatic tollgate according to any one of claims 31 and32, wherein said electromagnetic wave absorber has a multi-layerstructure which has impedance higher in an incident side ofelectromagnetic wave than impedance in the opposite side.
 34. Anelectronic device, wherein an electronic element mounted on a printedwiring board is sealed with a resin containing an electromagnetic waveabsorber.
 35. A printed wiring board comprising a wiring circuit on aninsulation board, wherein a layer having an electromagnetic waveabsorber is formed on at least one of a surface of said insulation boardhaving said wiring circuit and on a surface opposite to said surfacehaving said wiring circuit.
 36. An electronic equipment casing, whereinan electromagnetic wave absorber is formed on an inner peripheralsurface of a metal casing having an opeing portion.
 37. An automatictollgate comprising a tollgate roof; an entrance portion antennaarranged in an entrance side to a vehicle passing through the tollgate;an exit portion antenna arranged in an exit side to the vehicle passingthrough the tollgate; an electronic toll collection system for sendingand receiving information between a road-side communication unit and anin-car unit mounted on said vehicle, wherein an electromagnetic waveabsorber comprising magnetic metal particles and ceramic is formed onsurfaces of said tollgate and a member near the tollgate which reflectsan electromagnetic wave.